1. Field of Invention
This invention relates to an improved tachometer and, more particularly, a tachometer of the type for use in measuring and comparing the angular velocities of at least two wheels of a vehicle in motion and providing output signals related to the angular velocities.
2. Prior Art
Increasing demand placed on the safety of the operation of motor vehicles in recent years lead industries to place greater emphasis to finding ways to improve the brake systems of vehicles. In connection with this there have been substantial research and developement efforts focused on the dynamic control of the brake systems. As an important element, such a brake system requires suitable means that can sense and measure the speed of the wheel accurately and reliably and generate appropriate output signals. For such purpose generally tachometers have been used to sense and measure the angular speed of the wheels of a vehicle in motion and provide DC voltage output signals which are directly related to the angular speeds of the wheels.
Typically, a conventional tachometer includes transducing means for sensing the angular speed and providing a pulse train, the repetition rate of which varies in direct proportion to the change in the angular speed of the wheel. The pulse train so generated is frequency doubled and integrated to provide an output DC signal for the associated wheel. Two DC outputs obtained in the aforementioned manner for two wheels of a vehicle in motion are then usually compared and applied to appropriate terminals.
While the prior art tachometer provides satisfactory performance, yet there is a great need for improving the circuitry to provide a more accurate and reliable output signal and simplify the circuitry for ease of manufacture and for reducing the cost of the end product.